1. Field of the Invention
The present invention relates to a color reproduction system which has color space data conversion formulas, their related formulas, parameters, etc. which are established in a hierarchical structure, and which allows a desired color space data conversion formula, etc. to be selected under various given input and output conditions for facilitating the reproduction of highly accurate colors.
2. Description of the Related Art
In recent years, there have widely been used color reproduction systems for reading a color image from an original document such as a photograph, a paint, or the like or processing color image data supplied from an image input device and either displaying a color image on a cathode-ray tube (CRT), outputting a color image as a hard copy from a printer, or printing a color image with a press plate. It is desirable to be able to obtain a color image of desired color tones irrespective of different output mediums and processing steps.
A printed material is produced according to a number of processing steps. More specifically, color separation films of Y, M, C, K are generated on the basis of color image data supplied from an image input device, and presensitized plates are exposed to color images through the color separation films. Then, the color images on the presensitized plates are developed, and the presensitized plates are set on a printing press to produce a printed material. The colors on the printed material which are finally produced depend on various printing conditions including the paper, inks, and water used, the type of the printing press, and the screen ruling and dot shape which are employed for the formation of dot-matrix images. In the field of printing industry which requires the above complex processing steps and conditions, there has been a demand for a system or process which displays color image data processed as desired on a CRT or the like for the user to confirm the final image quality of a printing material on the CRT or the like with high accuracy.
One prior art system which meets the above demand is a color reproduction system disclosed in U.S. Pat. No. 4,500,919. The disclosed color reproduction system comprises means for determining tristimulus appearance signals as common color data from a colored original document, means for effecting aesthetic correction on the tristimulus appearance signals, means for displaying a corrected color image based on the corrected tristimulus appearance signals, and means for selecting color materials for a hard copy to obtain reproduction signals which colorimetrically match the displayed color image. A combination of color materials selected by the color material selecting means is printed, and the printed color materials are measured by a colorimeter. The reproduction signals are then corrected based on the measured data to achieve a match between the printed color image and the displayed color image.
Another conventional color reproduction effort is a color reproduction process based on visual adaptation which is disclosed in International Patent Publication WO 92/17982. It is known that even if the colors of two printed materials colorimetrically match, the colors of the two printed materials are not necessarily visually perceived identically because of the color of the support layer of the printing material and the illuminating conditions. In view of such a fact, the disclosed color reproduction process achieves a more accurate color match by equalizing the white dots of the printed color image to those of the displayed color image in addition to the process of the color reproduction system disclosed in U.S. Pat. No. 4,500,919.
While both of the above conventional attempts are capable of reproducing colors accurately if the only matching condition is the color materials, for example, they are not effective in applications where complex conditions are involved, such as those encountered in producing a printed material.
For producing a printed material, it is necessary to establish not only color materials, but also output conditions including the type of the support layer of a printed material, the number of colors to be printed, a black printer quantity, and a screen ruling, and also printing press conditions including a printing order, a printing pressure, color material quantities, and a printing speed. It has been difficult for the conventional color reproduction arrangements to print color images highly accurately under the above wide range of printing conditions.